Hydraulic drive



Aug. 14, 1945. I R.- OBTRESAI. 2,381,923 A y HYDRAULI'C DRIVE l 'Filed Nov. 25, 1940 Inventor: Roerf Ol; 're'scLZ ATTORNESS f Patented Aug. 14. 194s `v HYDRAULIC DRIVE Robert Obtresal, Magdeburg, Germany; vested 1n the Alien Property Custodian Application November 23, 1940, Serial No. 366,840 In Germany June 15, 1939 2 claims.

'I'his invention relates to hydraulic drives .anu refers more particularly to a device'regulating the speed of a drive actuated by hydraulic means. This device may be used in conjunction with all p machines wherein the speed of a driven body is subjected to certain variations resulting from changes in the resistance opposing the movement of the actuated body. vHowever, the device constituting the subject matter of the present invention is particularly applicable to machine tools, the feed movement of which is actu- .ated by a hydraulic drive, and n which the speed of the feed movement is dependent upon the feed resistance.

. An object of the present invention is to eliminate this dependency between the speed of the drive and the resistance by the provision -of a` special regulating device.

Another object is the provision of a regulating device for hydraulic ydrives of machine tools andthe like which makes it possibleto maintain a substantially uniform speed of the drive `or of the feed movement despite changes in tm.

adjustable at will and which may -be usedfor -any desired step-wise variation in the speed of the drive or the feed movement.

In accordance with the present invention, this throttle valve is connected with an automatically operable regulating device which is situated in that part of the hydraulic circuit which suppliesl the' operating fluid to the driving mechans The regulating device varies the amount of fluid flowing to the driving mechanism depending upon the difference in fluid pressure prevailing on both sides of the throttle valve, and upon an additional force which maintains constant this difference in pressure. U

By means of this regulating device, the difference in pressure between the. two sides of the throttle and valve and, consequently, the amount of fluid flowing through the throttle valve are always maintained constant'and entirely independent oi the specific amount of pressure,ex isting on any one side of' the throttle valve. Therefore, the resistance exerted upon the movable part of the machine has no influence whatever upon this pressure difference. Since the Speed of the drive is determined solely by the amount of fluid supplied to it and since this amount is maintained constant by the regulating device, the speed ofthe drive or of the feed movement will always remain the same irrespective of any possible variations in the resistance opposing thev movement.

The invention will appear more clearly by the following detailed description when taken in connection with the accompanying drawing showing, by way of example, an embodiment of the inventive idea, as applied to feed drives of machine tools. V

In the drawing, there is illustrated a hydraulic drive constructed in accordance with the principles ofthe present invention.

The hydraulic drive shown in the drawing includes a cylinder 25 containing a piston 26 which is connected on one side with `a piston rod 21. so that the two side surfaces of the piston 28 are of different size. -The comparatively wide piston rod 21 extends through a lsuitable opening formed in the cylinder 25 and is attached to the carriage of the machine tool. The fluid used to loperate the piston 28 is circulated by a pump 34 situated within a container 28. A pipe 35 connected to the pump 34 is provided with a Vbranch pipe 36 which leads to a regulatable throttle valve 31. The pipe 35 communicates with the space 32a within a cylinder 32 of the regulating device. The cylinder 32 contains a piston 39 which is loaded by a spring 4I. Consequently, the regulating device 32, 39 is inserted in that part of the hydraulic circuit which transmits fluid under pressure to the cylinder 25.

.A pipe 35-a is in communication with the pipe 35 close to the pump 34. This pipe 35-a leads to a relief valve 35-b which is provided with a 'pipe 35-c communicating with the interior of the container 28. y

A pipe 3l connects the space 32h within the container 32 with a three way cock or change over valve 30. The valve 30 is connected with the space 25a within the cylinder 25 by a pipe 29 and has a valve body provided with threey passages which connect the pipe 29 .with the pipe 3i in the position shown in'Flgure 2. The other end of the cylinder 25 is in communication with the pipe 35 by a return flow pipe 33. Another pipe 29a leads from the valve 38 to the 'interior of the container 28 for the fluid.

When the v'alve 38 is turned clockwise through the space 25a of cylinder 25 is connected through pipe 28, valve 30 and pipe 29a with the container 28, and pipe 3| is closed.

When the change-over valve 30 is thus positioned. fluid forced, by pump 34 through pipes 35 and 33. impinges on the left-hand face of piston 26 driving it toward the right and such movement forces the liquid from the space 25a back to the container 28, through pipes 29 and 29a.

The throttle valve 31 is connected with the space 92h within the cylinder 32 by the pipe 38. The regulating device 32, 39 includes a spring 4| which presses against the piston 39 and which maintains the piston in a position in whichit partly covers the opening 3|a of the pipe 3|.

Thek device is operated as follows:

The pump 34 causes a ow of liquid under' pressure through the pipe 35,` the kpipe 36, the throttle valve 31, the pipe 38, the space 32h within the container 32, 'the pipe 3|, the valve 30 and the pipe 29 into the space 25a of the cylin-I vailing on both sides of the throttle valve 31 determines the amount of the liquid which operates within the cylinder 25.

' If the resistance W opposed to the'movement of the tool carriage remains unchanged, a fluid pressure will Aarise within the space a and in the pipes 29 and 3|, which is necessary to overi come the resistance W and the pressure exerted upon the annular surface of the piston 26 around the piston rod 21.

The pump 34 transmits the fluid under a higher pressure through the pipe 35 into the space` 32a within the cylinder 32. I'his higher pressure, which is also exerted' upon the adjacent surface of the piston 39, is balanced by the force P of the spring 4| and the pressure of the iluid upon the surface 42 of the piston 39, so that the piston 39 is maintained in the illustrated position. There is an equilibrium when fluid pressure in the space 32a to the right of the piston 39 is equal to the force P of the spring 4| plus fluid pressure in the space 32h to the left of the piston 39.

In the illustrated position, the edge of the sur-v face 42 of the piston 39 covers a portion of the opening 3m of the pipe 3|. Any movement of the piston 39 will change, therefore, the operative cross sectional area of the opening 3|a. The

area of the opening 3 la is varied depending upon the resistance opposing the movement of the piston 26 and, consequently, the fluid pressure in the pipes 29 and 3|.

If, for instance, the resistance W exerted upon the piston 26 is increased, then the pressure of the fluid in the pipes 29, 3|, and 38 is increased also. The piston 39 is then moved to the right, so that the operative area of the opening 3|a shown above has been given by way of illustration and not byway of limitation and that the structures above described are subject to wide variation and modification without departing from scope or intent of the invention. All/of such'variations and modifications are to be included within the scope of the present invention.

What is claimed is:

l. In a hydraulic drive having a movable member, a piston rod connected with said memb'er, a piston connected with said piston rod, and a cylinder enclosing said piston; a device for the circulation of the fluid to and from said cylinder, 'said device comprising a container for the iiuid, a pump contacting the fluid within said container, a change over valve, a pipe connecting said change over valve l:with one side of said cylinder, aregulating device including a hollow casing having an opening formed therein through which the fluid may flow, a reciprocable piston situated Within said casing, said opening being so located relatively to the last-mentioned piston that it.may be partly covered thereby to vary the amount of fluid transmitted through the opening, a throttle valve, a pipe connecting -one side of said'throttle valve with the space within said casing on one side 'of the last-mentioned piston, another pipe connecting the other side oi said throttle valve with the space within said casing on the other side of the last-mentioned piston and with said pump, a spring situ- .ated within said casing and within the space with the last-mentioned pipe to supply uid is increased, and the already existing difference n in pressures prevailing in the space 32h and in thepipes 29 and 3|, is diminished. However,

38 and in the pipe 36 remains the same, so that the `amount of fluid flowing through the throttle valve| 31 and, consequently, the speed of movement of the piston 26 are not changed.

If the resistance W becomes smaller, the piston the difference in pressures prevailing in the pipe I cylinder port.

under pressure to said one side of the cylinder.'

a pipe Aconnecting the other side of the cylinder with the third-mentioned pipe; and a pipe connectingsaid change-over .valve with the container, the change-over valve being so constructed and disposed thatwhen it is in one position Vit connects the pipe from the valve to the cylinder with the pipe from the opening of the casing, and in another position it connects the pipe to the cylinder with the .pipe to the container.l

2. A regulating device, in combination with a piston, driven .by a. fluid, in a. cylinder having two ports o'n opposite sides of said piston respectively, and a container for the fluid provided with a pump. to supply the fluid tothe piston. consisting of a pipe from said pump, having three branches, a throttle valve having its inlet connected with one branch, a casing connected at one end with a second branch, 'the outlet of the throttle valve being connected with the other end of the casing, a reciprocable piston in said casing between the twoconnections and having a spring urging it toward the firstl mentioned connection, an outlet from said casing so related to said casing piston that vit may be partially covered thereby to vary the amount of fluid passing through -said outlet, a pipe connected with said outlet, means adapted to connect, alternatively, said'last mentioned pipe with one of the cylinder ports, and said cylinder port with said container, and a pipe connecting the third branch of the pipe from the pump with the other ROBERT OBTRESAL. 

